The desire to reduce automotive fuel consumption and emissions has been well documented. Therefore, electrified vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. In general, electrified vehicles differ from conventional motor vehicles because they are selectively driven by one or more battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to propel the vehicle.
Some electrified vehicles, such as hybrid electric vehicles (HEV's), are equipped with an engine and an electric machine that are both capable of supplying torque for powering the vehicle drive wheels. A significant amount of vehicle exterior noise is created during normal engine operation, engine start/stop, and engine idling. This noise is often the result of mechanical motion of components, fuel combustion, air intake, and exhaust processes of the engine. In some situations, this noise may be undesirable to the vehicle operator and nearby pedestrians.